The present invention relates to a fin of heat exchanger and a method of making it. In particular, the invention has made the thinning of the fin possible because of an improvement in the corrosion resistance without lowering the heat transferability as a fin. The fin of the invention is suitable particularly for the heat exchangers used under conditions of an intensely corrosive environment, as in the case of cars etc.
For the radiating fin used for the shell and tube type heat exchanger, strength and corrosion resistance are required together with heat transferability. For instance, the heat exchanger for a car uses a radiator for cooling the engine and a heater for air-conditioning. In all cases, a copper core fitted up with the fins between a plurality of tubes through which the heat exchange medium circulates is used and tanks are installed at both ends of said core through washer plates. Namely, in the radiator, as shown in FIG. 1, the core (3) is constructed by fitting up with the corrugated fins (2) between a plurality of up- and downward tubes (1) through which the heat exchange medium circulates, the washer plates (4a) and (4b) are provided at both ends of tubes (1) in said core (3), and the tanks (5a) and (5b) are installed onto said washer plates (4a) and (4b). Besides, in the diagram, numerals (6) and (7) indicate the entrance and exit for refluxing of the heat exchange medium and numerals (8) and (9) indicate the injection and ejection ports of the heat exchange medium, respectively.
For such Cu-based core of radiator, brass tubes and Cu or Cu alloy corrugated fins are used generally, and the fins are fitted up between tubes by a type soldering called core burning. For the fin, Cu or Cu alloy strip having a thickness of 0.025 to 0.060 mm is used, and, in order to improve the strength and the heat resistance, small amounts of Sn, Ag, Cd, P, Zr, Mg, etc. are added within a range not lowering the heat transferability. Moreover, on the radiator having a Cu core, black paint is coated for the purpose of preventing the dazzlement, but this treatment is confined only to the outer surface of radiator and the thickness is also confined to less than 10 .mu.m, since the thicker film is harmful to the radiation of fin section.
In recent years, a large quantity of chlorides such as NaCl etc. has been scattered on the road for the purpose of melting snow etc., and the corrosion of the body of car by these chlorides is taken seriously. The fret of the fin is intense also with the heat exchangers for car such as radiator, air conditioner, etc., and the lowering in the radiation ability has become a subject of discussion. For this reason, the use of corrosion-resistant alloys such as Cu-Ni-based one etc. was investigated for the fin, but, because of the low heat transferability, the thickening became necessary to achieve the predetermined performance, which led to the high price and the increase in weight. Moreover, with conventional materials, the thickening having made allowance for the margin to corrosion and the painting for the prevention from corrosion brought also about similar results making it impossible to fit for practical use.
On the other hand, the lightening in weight of car is desired from a view point of energy conservation. The lightening in weight is desired also with the heat exchanger being parts of the car. However, it has been difficult technically to satisfy both the measures against salt damage aforementioned and the requirement of lightening simultaneously.